Next High Frequency Improvement by Using Frequency Dependent Effective Capacitance

ABSTRACT

A connector is provided for simultaneously improving both the NEXT high frequency performance when low crosstalk plugs are used and the NEXT low frequency performance when high crosstalk plugs are used. The connector includes a first compensation structure provided on an inner metalized layer of the PCB at a first stage area of the PCB, and a second compensation structure, provided at a second stage area of the PCB, for increasing compensation capacitance with increasing frequency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority as a continuation of U.S. patentapplication Ser. No. 11/657,024, filed Jan. 24, 2007, which issued asU.S. Pat. No. ______, which in turn is a continuation of U.S. patentapplication Ser. No. 10/845,104, filed May 14, 2004, which issued asU.S. Pat. No. 7,190,594. The entire contents of the proceedingapplications are incorporated by reference in there entirety as if setforth fully herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to near-endcrosstalk (NEXT) compensation in connectors and, more particularly, to atechnique of canceling or reducing NEXT in a multi-stage compensatedsystem by providing frequency dependent effective capacitance.

2. Discussion of the Related Art

Noise or signal interference between conductors in a connector is knownas crosstalk. Crosstalk is a common problem in communication devicesusing connectors. Particularly, in a communication system where amodular plug often used with a computer is to mate with a modular jack,the electrical wires (conductors) within the jack and/or plug producenear-end crosstalk (NEXT), i.e., a crosstalk over closely-positionedwires over a short distance. A plug, due to its configuration or to themanner in which cordage is terminated to it, can produce a highcrosstalk or a low crosstalk. A plug with a high crosstalk is hereinreferred to as a high crosstalk plug, and a plug with a low crosstalk isherein referred to as a low crosstalk plug.

U.S. Pat. No. 5,997,358 issued to Adriaenssens et al. (hereinafter “the'358 patent”) describes a two-stage scheme for compensating such NEXT.The entire contents of the '358 patent are incorporated by reference.Further, the subject matters of U.S. Pat. Nos. 5,915,989; 6,042,427;6,050,843; and 6,270,381 are also incorporated by reference.

The '358 patent reduces the NEXT (original crosstalk) between theelectrical wire pairs of a modular plug by adding a fabricated orartificial crosstalk, usually in the jack, at two stages, therebycanceling the crosstalks or reducing the overall crosstalk for theplug-jack combination. The fabricated crosstalk is referred to herein asa compensation crosstalk. This idea is typically implemented usingcapacitive and/or inductive compensation in two stages. This idea can berealized, for example, by crossing the path of one of the conductors ofone of the pairs of a pair combination to be compensated, within theconnector twice, thereby providing two stages of NEXT compensation. Thisscheme is more efficient at reducing the NEXT than a scheme whereby thecompensation is added at a single stage, especially when, as is usuallythe case, the compensation can not be introduced except after a timedelay.

Although effective, the NEXT compensating scheme of the '358 patentsuffers a drawback in that the NEXT margin relative to theTelecommunications Industry Association (TIA) limit line deteriorates atlow frequency (below approximately 100 MHz) when a high crosstalk plugis used with the jack, and at high frequency (beyond approximately 250MHz) when a low crosstalk plug is used with the jack. More specifically,when the net compensation crosstalk in a two-stage compensated jack isless than the original crosstalk (i.e. when a high crosstalk plug isinserted into the jack), the plug-jack combination is said to beunder-compensated, and the resultant NEXT frequency characteristic willbuild-up to a peak at low frequencies before a null sets in at afrequency point determined by the inter-stage delays and the magnitudesof the compensating stages. Then the slope of the NEXT magnitudefrequency response changes from a shallow slope before the null to asteep slope after the null, thereby causing the NEXT to deterioraterapidly at high frequencies, i.e., at frequencies beyond these nulls.

On the other hand, when the net compensation crosstalk in such a jack ismore than the original crosstalk (i.e. when a low crosstalk plug isinserted), the plug-jack combination is said to be overcompensated, andthe resultant NEXT frequency characteristic will not have a null, butthe slope of the NEXT frequency characteristic will gradually increasetending towards 60 dB/decade at very high frequencies, far exceeding theTIA limit lope of 20 dB/decade.

Thus, while the low frequency margin (low frequency performance of theconnector), when a high crosstalk plug is used with the jack, can beimproved by increasing the compensation level, such an action would leadto further deterioration of the high frequency margin (high frequencyperformance of the connector) when a low crosstalk plug is used with thejack. Conversely, while the high frequency margin, when a low crosstalkplug is used with the jack, can be improved by decreasing thecompensation level, such an action would lead to further deteriorationof the low frequency margin when a high crosstalk plug is used with thejack.

Therefore, there exists a need for a technique capable of simultaneouslyreducing or canceling NEXT at high frequencies when low crosstalk plugsare used, and at low frequencies when high crosstalk plugs are used.

SUMMARY

The present invention overcomes the problems and limitations of therelated art techniques of reducing NEXT in connectors. Particularly, thepresent invention provides a multi-stage crosstalk compensation schemein which the resultant capacitive coupling is biased in such a way as toreduce the overall compensation level as the frequency increases,thereby improving significantly the high frequency NEXT performance ofthe connector without degrading the low frequency NEXT performance. Thisis achieved by providing a first stage compensation structure that has arelatively flat effective capacitance response as the frequencyincreases, while providing a second stage compensation structure thathas an increasing effective capacitance response as the frequencyincreases.

The present invention improves both the low frequency (e.g., 1-100 MHz)crosstalk performance and the high frequency (e.g., 250-500 MHz; or 500MHz and greater) crosstalk performance of modular outlets and panels.

These and other objects of the present application will become morereadily apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention and wherein:

FIG. 1 shows a series inductor-capacitor combination stricture used inthe present invention;

FIG. 2 is a perspective view of a simplified printed circuit board (PCB)showing an example of how the series inductor-capacitor combination ofFIG. 1 can be implemented according to a first embodiment of the presentinvention;

FIG. 3 is a graph showing a simulated example of the effectivecapacitance v. frequency response of the PCB structure shown in FIG. 2;

FIG. 4A is a side view of a connector according to the first embodimentof the present invention;

FIG. 4B is a top plan view of the PCB and NEXT compensation elements ofFIG. 4A according to the first embodiment of the present invention;

FIG. 5 shows an example of the structure of an interdigital capacitoraccording to a second embodiment of the present invention;

FIG. 6 is a graph showing a simulated example of the effectivecapacitance v, frequency response of interdigital capacitors withdifferent length/width ratios;

FIG. 7A is a side view of a connector according to the second embodimentof the present invention;

FIG. 7B is a top plan view of the PCB and NEXT compensation elements ofFIG. 7A according to the second embodiment of the present invention;

FIG. 8 is a perspective view of a simplified PCB showing how the seriesinductor-capacitor combination of FIG. 1 can be implemented according toa third embodiment of the present invention;

FIG. 9 is an example of a folded elongated interdigital capacitoraccording to a fourth embodiment of the present invention;

FIG. 10 is a perspective view of a simplified PCB showing how the seriesinductor-capacitor combination of FIG. 1 can be implemented according toa fifth embodiment of the present invention;

FIG. 11 is a graph comparing, as an example, the effective capacitancev. frequency responses of the NEXT compensated PCBs of the variousembodiments of the present invention;

FIG. 12A is a side view of a connector according to a sixth embodimentof the present invention; and

FIG. 12B is a top plan view of the PCB and NEXT compensation elements ofFIG. 12A according to the sixth embodiment of the present invention.

DETAILED DESCRIPTION

Reference will flow be made in detail to the preferred embodiments ofthe present invention, examples of which are illustrated in theaccompanying drawings. In the present application, a ‘stage’ is referredto a place of compensation, which occurs at a compensation delay point.The present invention provides various configurations of printed circuitboards (PCBs) which can replace the printed wiring board of FIG. 7A inthe '358 patent.

The present invention provides a compensation stricture at a secondstage of a multi-stage NEXT compensation system for a connector. Thissecond stage has an increasing effective capacitance response as thefrequency increases. This can be achieved by using a seriesinductor(L)-capacitor(C) combination structure, a high length/widthratio interdigital capacitor, an elongated folded interdigitalcapacitor, or an open-circuited transmission lines in a connector,according to the different embodiments of the present invention.

FIG. 1 shows a series L-C combination structure according to a firstembodiment of the present invention. The equation for the effectivecapacitance (C_(eff)) for this series L-C combination structure is asfollows:

${Ceff} = \frac{C}{1 - {\left( {2\pi \; f} \right)^{2}{LC}}}$

where f is the frequency, C represents the capacitance of the capacitor;and L represents the inductance of the inductor. As can be seen fromthis equation, the effective capacitance C_(eff) increases withfrequency at frequencies that are less than the resonant frequencyf_(res) of the series L-C combination. The resonant frequency f_(res) isdefined as follows:

$f_{res} = \frac{1}{2\pi \sqrt{LC}}$

According to the present invention, L and C are chosen such that theresonant frequency f_(res) occurs above the highest operating frequencyof the bandwidth of interest. This allows the effective capacitance toincrease as the frequency increases up to the resonant frequencyf_(res).

FIG. 2 is a perspective view of a simplified PCB) showing how the seriesL-C combination structure of FIG. 1 is implemented according to a firstembodiment of the present invention. As shown in FIG. 2, the series L-Ccombination structure of FIG. 1 is provided with a PCB. Here, details ofthe printed circuits are not shown. The inductor L in this example isimplemented with a spiral inductor having a spiral structure residing ona top surface of the PCB. The capacitor C in this example is implementedwith a capacitor structure composed of two interdigital capacitorselectrically in parallel to each other residing at inner layers of thePCB. A interdigital capacitor is a capacitor having a co-planararrangement of two inter-meshed metal combs each at a differentpotential, and is known. The capacitor C is electrically connected tothe inductor L through a conductive via 8 such as a plated through hole.Note that for the purpose of the first embodiment of this invention, theseries capacitor of FIG. 1 can also be implemented using a simpleparallel plate capacitor configured on two layers of the PCB.

FIG. 3 is a graph showing a simulated example of the effectivecapacitance v. frequency response of the PCB structure shown in FIG. 2.This graph is simulated by using a known simulation software “hfss”offered by Ansoft, Inc. With the capacitance values normalized to 1 pFat 100 MHz, the graph shows that the effective capacitance of the PCBshown in FIG. 2 increases as the frequency increases. A similar responseexists had the capacitor been a simple parallel plate capacitor.

FIGS. 4A and 4B demonstrate how to apply the series L-C combinationstructure in this example to compensate for the 1-3 pair NEXT in aconnector, according to the first embodiment. FIG. 4A is a side view ofa connector according to the first embodiment of the present invention,and FIG. 4B is a top plan view of the PCB and NEXT compensation elementsof FIG. 4A according to the first embodiment of the present invention.

Referring to FIGS. 4A and 4B, the connector includes spring contacts 30having crossovers 14, and a PCB 10. A plug 20 is to mate with theconnector. The plug 20 can be a modular plug such as one used at the endof a phone line or a patch cord used to connect a personal computer to awall outlet. The contacts 30 can be soldered or press-fitted intoplated-through holes 32 located at the appropriate portions of the PCB10 and can be spring wire contacts. Moreover, the contacts 30 have acurrent carrying portion 30 b and a non-current carrying portion 30 a,where a boundary BD between these portions 30 a and 30 b are indicatedin FIG. 4A. The contacts 30 and the PCB 10 can be housed in a housingsuch as a modular jack, so that when the plug 20 enters the jack, theelectrical contacts on the plug 20 mate with the electrical contacts onthe PCB 10 via the contacts 30.

The PCB 10 is a multi-layered board made of resin or other materialknown suitable as a PCB material. In this example, the PCB 10 iscomposed of three substrates (S1-S3) and four metalized layers (ML1-ML4)alternatingly stacked up. More specifically, the substrates and themetalized layers are stacked up in the following order (from top tobottom): ML1, S1, ML2, S2, ML3, S3, and ML4. The metalized layersML1-ML4 each represent metal conductive patterns formed on the uppersurface of the substrate directly below the corresponding metalizedlayer. Certain parts of the metalized layers are interconnected witheach other for electrical connection through one or more conductive vias32 such as plated through holes. The spring contacts 30 as shown areformed above the first metalized layer ML1.

The spring contacts 30 can be a plurality of wire pairs P, each wirepair P including contacts designated as a ring (r) and a tip (t). InFIG. 4B, four pairs are provided and they are (t1, r1), (t2, r2), (t3,r3), and (t4, r4). The ring is known to be a negatively polarizedconductor and the tip is known to be a positively polarized conductor.

First and second pairs of interdigital capacitors 40 a and 40 b act ascapacitive compensation for the first stage NEXT compensation and areformed respectively on or as part of the second and third metalizedlayers ML2 and ML3 of the PCB 10. In this example, the jack springs in asection 30 b are arranged after the cross-over at 14 to contributeinductive compensation also as part of the first stage compensation. Thefirst pair of interdigital capacitors 40 a on the layer ML2 isduplicated on the layer ML3 as the second pair of capacitors 40 b. Thefirst pair of interdigital capacitors 40 a is made up of capacitors 40at and 40 a ₂ both disposed on the layer ML2. The second pair ofinterdigital capacitors 40 b is made up of capacitors 40 b ₁ and 40 b ₂both disposed on the layer ML3. The ends of the first capacitor 40 a ₁in the first pair are in electrical contact with the rings r3 and r1respectively through a pair of plated through holes 48 a and 48 b. Theends of the second capacitor 40 a ₂ in the first pair are in electricalcontact with the tips t1 and t3 respectively through a pair of platedthrough holes 48 c and 48 d. The second pair of interdigital capacitors40 b are capacitors 40 b ₁ and 40 b ₂ both disposed on the layer ML3 inthe same manner as the first pair of interdigital capacitors 40 a.Through plated through holes 48 a and 48 b, the capacitors 40 a ₁ and 40b ₁ are electrically connected in parallel. Similarly, through platedthrough holes 48 c and 48 d, the capacitors 40 a ₂ and 40 b ₂ areelectrically connected in parallel.

Furthermore, series L-C combination structures that act as second stageNEXT compensation strictures are provided at the PCB 10. The firstseries L-C combination structure includes a spiral inductor 44 and firstand second interdigital capacitors 46 a and 46 b. The spiral inductor 44is disposed on or above the first metalized layer ML1, whereas the firstand second interdigital capacitors 46 a and 46 b are disposedrespectively on the second and third metalized layers ML2 and ML3. Inthe similar manner, the second series L-C combination structure includesa spiral inductor 54 and third and fourth interdigital capacitors 56 aand 56 b. The spiral inductor 54 is disposed on or above the firstmetalized layer ML1, whereas the third and fourth interdigitalcapacitors 56 a and 56 b are disposed respectively oil the second andthird metalized layers ML2 and ML3. In this example, the first and thirdcapacitors 46 a and 56 a on the layer ML2 are duplicated on the layerML3 as the second and fourth capacitors 46 b and 56 b, respectively.Through plated through holes 33 a and 32 c, the capacitors 46 a and 46 bare connected electrically in parallel. Through plated through holes 33b and 32 f, the capacitors 56 a and 56 b are connected electrically inparallel.

In the present application, “duplicated” with respect to thecompensation capacitors means identically copied on all the designatedmetalized layers. For instance, the capacitors 40 a would have theidentical shape and size and would be vertically aligned with thecapacitors 40 b. The reason for duplicating the interdigital capacitorsis to increase the capacitance without having to increase the foot-print(surface coverage). Also larger foot-print interdigital capacitors couldbe used without the need for this duplication. On the other hand, if theprinted circuit board was constructed with more metalized layers, theinterdigital capacitors can be duplicated on more than two metalizedlayers to make the foot-print even smaller if desired. Note that withinthe spirit of the first embodiment, parallel plate capacitors could beused in place of the interdigitated capacitors 46 a, 46 b, 56 a and 56b. Also the first stage capacitors 40 a and 40 b could also have beenparallel plate capacitors, as used in, e.g., FIG. 10 to be discussedlater.

The inductor 44 is connected in series with each of the first and secondinterdigital capacitors 46 a and 46 b through the plated through hole 33a. One end of the inductor 44 is electrically connected to the tip t3through a plated through hole 32 b. One end of each of the first andsecond capacitors 46 a and 46 b is electrically connected to the ring r1through the plated through hole 32 c. In a similar manner, the inductor54 is connected in series with each of the third and fourth interdigitalcapacitors 56 a and 56 b through the conductive via 33 b. One end of theinductor 54 is electrically connected to the tip t1 through a platedthrough hole 32 e. One end of each of the third and fourth capacitors 56a and 56 b is electrically connected to the ring r3 through the platedthrough hole 32 f.

According to the present invention, the use of the series L-Ccombination structures for the second stage NEXT compensation of a twostage compensation approach, which is shown in this is example for the1-3 pair combination, improves performance at high frequencies if theplug 20 is a low crosstalk plug and improves performance at lowfrequencies if the plug 20 is a high crosstalk plug. An explanation onhow this works is as follows.

NEXT is attributed to two factors: capacitive coupling and inductivecoupling. The close proximity of two wires creates capacitive coupling,whereas the current flowing through these wires creates inductivecoupling. Thus, the plug 20 introduces both the capacitive coupling andinductive coupling as it mates with the contacts 30. Both of thesefactors add to generate near end crosstalk or NEXT.

To reduce or compensate for the NEXT, two stages of compensation aregenerally used. The first stage is phased in opposition to the plug NEXTwhile the second stage is phased in the same direction of the plug NEXT.This is known and disclosed in the '358 patent. The direction of thecompensation relative to that of the plug is illustratively shown asarrows V1 to V5 in FIG. 4A.

Also, crosstalk generated at the far end of a connector is called FEXT.To compensate for this parameter, some portion of the normal NEXTcompensation must include an inductive component. This component is partof the first stage of the two stage compensator described here. Thisoccurs in the section 30 b of the jack spring wires just beyond thecrossover 14. In this region of compensation, the compensation isrelatively stable with frequency.

A significant part of the first stage compensation for NEXT iscapacitive compensation and is provided by using the capacitors 40 a and40 b. In FIGS. 4A and 41B, this part of the first stage is at a minimaldelay from the original crosstalk, being at a portion of the PCB 10where electrically it is directly connected, via the non-currentcarrying portion 30 a of the contacts 30, to where the contacts of theplug 20 intercept the contacts 30. The net first stage compensationwhich is the capacitive portion before crossover 14 plus the inductiveportion just beyond the crossover 14 is in opposition to the crosstalkgenerated in the plug. The second stage is at a further delay from thefirst stage, being at a portion of the PCB 10, which is at some distancefrom where the contacts of the plug 20 intercept the contacts 30 via thecurrent carrying portion 30 b of the contacts 30. It has a compensationdirection which is in the same direction of the plug crosstalk.

The interdigital capacitors 40 a and 40 b are placed on the innermetalized layers as part of the first stage. The series L-C combinationstructures are placed at the second stage. The magnitude of the firststage compensation, which is mostly capacitive and without an addedseries inductive element, is made relatively flat with frequency. Thesecond stage capacitive compensation, on the other hand, is made toincrease with frequency by placing the series L-C combination stricturesin the PCB layers. As a result, the net compensation crosstalk(fabricated crosstalk) of the connector, which is comprised of the firststage compensation crosstalk minus the second stage compensationcrosstalk, declines with increasing frequency. In other words, the netcompensation crosstalk becomes variable depending on the frequency, suchthat the present invention provides a lower-level of compensationcrosstalk at a high frequency than would normally exist without theseries inductor in place. This minimizes crosstalk over-compensation inthe connector at high frequencies. Also the frequency dependentcompensation provides a higher-level of compensation crosstalk at a lowfrequency to minimize crosstalk under-compensation at low frequencies inthe connector. By providing the low-level compensation crosstalk at ahigh frequency, the present invention improves the high frequency marginof the connector when a low crosstalk plug is inserted into the jack. Onthe other hand, by providing the high-level compensation crosstalk at alow frequency, the present invention improves the low frequency marginof the connector when a high crosstalk plug is inserted into the jack.

Another method of achieving an increase in effective capacitance with anincrease in frequency is to exploit the self resonance characteristic ofan interdigital capacitor described in an article entitled “InterdigitalCapacitors and their Application to Lump-element Microwave IntegratedCircuits” by Gary D. Alley, IEEE Transactions on Microwave Theory andTechniques, Vol. MTT-18, No. 12, December 1970, pp. 1028-1033. In thearticle Alley teaches that an interdigital capacitor exhibits selfresonance at a frequency determined by its length-to-width ratio.

As shown in FIG. 5, an interdigital capacitor 70 includes first andsecond combs 70 a and 70 b that are intermeshed with each other, andterminals 72. The length (L) and width (W) of the interdigital capacitoris defined as shown. As the length-to-width ratio (L/W) of theinterdigital capacitor increases, the frequency at which it exhibitsself resonance decreases. This is manifested in a higher rate ofincrease in effective capacitance throughout the bandwidth of interestprovided that the frequency of resonance remains above that bandwidth.This is shown in FIG. 6, which is a graph showing the effectivecapacitance v. frequency response of interdigital capacitors withdifferent L/W ratios. This graph shows the result of simulation by thesoftware “hfss” offered by Ansoft, Inc. and compares the frequencydependence of different interdigital capacitor geometries as well as theparallel plate capacitor. As shown in FIG. 6, an elongated interdigitalcapacitor having the L/W ratio of 10.39 has the highest rate of increasein effective capacitance with respect to an increase in frequency, incomparison with interdigital capacitors with the L/W ratios of 1.27 and0.195 and in comparison with a parallel plate type capacitor. Allresponses in the graph are normalized to 1 pf at 100 MHz for thiscomparison.

The self resonance characteristic of an elongated interdigital capacitordiscussed above is used to provide NEXT compensation in a multi-stagecompensation system according to the second embodiment of the presentinvention. FIG. 7A is a side view of a connector according to thissecond embodiment of the present invention, and FIG. 7B is a top planview of the PCB and NEXT compensation elements of FIG. 7A. The secondembodiment is identical to the first embodiment, except that differenttypes of NEXT compensation elements are used. Particularly, the firststage compensation capacitors are implemented using first and secondparallel plate capacitors 50 and 51, and the second stage compensationelements are implemented using a first pair of elongated interdigitalcapacitors 57 a and 58 a and a second pair of elongated interdigitalcapacitors 57 b and 58 b. A parallel plate capacitor is a capacitorcomposed of two parallel metal plates each at a different potential, andis known.

The two plates (50 a and 50 b in FIG. 7A) of the first parallel platecapacitor 50 are respectively formed on the second and third metalizedlayers ML2 and ML3. In the same manner, the two plates of the secondparallel plate capacitor 51 are respectively formed on the second andthird metalized layers ML2 and ML3. The plate 50 a of the capacitor 50is connected to the ring r1 through the plated through hole 48 b. Theplate 50 b of the capacitor 50 is connected to the ring r3 through theplated through hole 48 a. Similarly, the plate 51 a of the secondparallel plate capacitor 51 is connected to the tip t1 through theplated through hole 48 c and the plate 51 b of the capacitor 51 isconnected to the tip t3 through the plated through hole 48 d.

The first pair of elongated interdigital capacitors 57 a and 58 a areformed as part of the metalized layer ML2, and the second pair ofelongated interdigital capacitors 57 b and 58 b are formed as part ofthe third metalized layer ML3. One end of each of the elongatedcapacitors 57 a and 57 b is electrically connected to the ring r1through the plated through hole 32 c, whereas the other end of each ofthe elongated capacitors 57 a and 57 b is electrically connected to thetip t3 through the plated through hole 32 b. Therefore, the interdigitalcapacitors 57 a and 57 b are electrically placed in parallel, to achievehigher capacitance. In the similar manner, one end of each of theelongated capacitors 58 a and 58 b is electrically connected to the ringr3 through the plated through hole 32 f, whereas the other end of eachof the elongated capacitors 58 a and 58 b is electrically connected tothe tip t1 through the plated through hole 32 e. Therefore thecapacitors 58 a and 58 b are electrically placed in parallel to achievehigher capacitance.

Accordingly, the magnitude of the first stage compensation capacitivecoupling is made relatively flat with frequency by placing the parallelplate capacitors at the first stage of the connector. The second stagecompensation capacitive coupling is made to increase with frequency byplacing the elongated interdigital capacitors with large L/W ratios atthe second stage of the connector. As a result, the net compensationcrosstalk of the connector declines with the increase of frequency.

In a third embodiment of the present invention, the methods of the firstand second embodiments are combined. Particularly, in the thirdembodiment, the second stage compensation elements are implemented usinga series L-C combination structure, where this structure as shown in,e.g., FIG. 8, includes a spiral inductor 72 connected in series with anelongated interdigital capacitor 74 with a large L/W ratio and disposedat the PCB 10. In other words, the connector of the third embodiment isidentical to the connector of the first embodiment shown in FIGS. 4A and4B, except that each of the second stage interdigital capacitors 46 a,46 b, 56 a and 56 b is elongated to have a large L/W ratio.

In a fourth embodiment and a fifth embodiment of the present invention,the method of the second and third embodiments can be implementedrespectively using a folded elongated interdigital capacitor in place ofthe high aspect ratio interdigital capacitor shown in FIG. 8. An exampleof a folded elongated interdigital capacitor is shown in an explodedview in FIG. 9.

More specifically, in the fourth embodiment, the two regular elongatedinterdigital capacitors 57 a and 57 b formed respectively at themetalized layers ML2 and ML3 of the PCB as shown in FIGS. 7A and 7B ofthe second embodiment are replaced with one folded elongatedinterdigital capacitor with its layers provided at the metalized layersML2 and ML3 as indicated in FIG. 9. In the same manner, the two regularelongated interdigital capacitors 58 a and 58 b formed respectively atthe metalized layers ML2 and ML3 of the PCB as shown in FIGS. 7A and 7Bof the second embodiment are replaced with one folded elongatedinterdigital capacitor with its layers provided at the metalized layersML2 and ML3 as indicated in FIG. 9.

The fifth embodiment is identical to the third embodiment, except thatthe regular elongated interdigital capacitor 74 shown in FIG. 8 of thethird embodiment is replaced with a folded elongated interdigitalcapacitor 78 as shown as FIG. 10. This folded elongated interdigitalcapacitor 78 has the same structure as the folded elongated interdigitalcapacitor shown in FIG. 9. Since the third embodiment is identical tothe first embodiment shown in FIGS. 4A and 4B, except for the use of theelongated interdigital capacitors shown in FIGS. 7A and 7B, the fifthembodiment simply is identical to the first embodiment shown in FIGS. 4Aand 4B, except that the interdigital capacitors 46 a, 46 b, 56 a and 56b are replaced with the folded elongated interdigital capacitors havinglarge L/W ratios.

More specifically, in the fifth embodiment, the two regular interdigitalcapacitors 46 a and 46 b formed respectively at the metalized layers ML2and ML3 of the PCB as shown in FIGS. 4A and 4B of the first embodimentare replaced with one folded elongated interdigital capacitor with itslayers provided at the second and third metalized layers ML2 and ML3(e.g., as indicated in FIG. 9). In the same manner, the two regularinterdigital capacitors 56 a and 56 b formed respectively at themetalized layers ML2 and ML3 of the PCB as shown in FIGS. 4A and 4B ofthe second embodiment are replaced with one folded elongatedinterdigital capacitor with its layers provided at the metalized layersML2 and ML3.

FIG. 11 is a graph comparing, as an example, the effective capacitancev. frequency responses of the first, fourth and fifth embodiments of thepresent invention. This graph shows the result of simulation produced bythe software “hfss” offered by Ansoft, Inc. and all responses in thegraph are normalized to 1 pf at 100 MHz for this comparison. As shown inFIG. 11, the combination of the spiral inductor and the folded elongatedinterdigital capacitor connected in series at the second stage accordingto the Fifth embodiment (response 80) yields an effective capacitanceincrease with frequency that is higher than what would be obtained withthe compensation schemes according to the first embodiment (response81), or fourth embodiment (response 82).

FIG. 12A is a side view of a connector according to a sixth embodimentof the present invention, and FIG. 12B is a top plan view of the PCB andNEXT compensation elements of FIG. 12B. As shown in FIGS. 12A and 12B,this sixth embodiment is identical to the second embodiment, except thatopen-circuited transmission lines 92 (92 a, 92 b, 92 c and 92 d) areused as the second stage compensation elements. In this case the firststage compensation capacitors are implemented using the parallel platecapacitors 50 and 51 as in the second embodiment, and the second stagecapacitive compensation elements are implemented using theopen-circuited transmission lines 92 on the second metalized layer ML2at the PCB 10. Resonance in this embodiment occurs at the frequencywhere the length of the transmission line 92 becomes equal to a quarterwavelength at the resonant frequency.

Although four layered PCB structures are illustrated, it should bereadily apparent that any other number of PCB substrates and/ormetalized layers may be used for the PCB(s). The resultant connector ofthe present invention can be associated with housings, insulationdisplacement connectors, jack spring contacts, etc. Also, the variousconfigurations and features of the above embodiments may be combined orreplaced with those of other embodiments. Where the capacitors ofinterdigital type are used, plate capacitors or discreet capacitors maybe used instead. Also, the inductors can be implemented using geometriesother than the circular spiral shown in FIG. 4B, such as oval spiral,square spiral, rectangular spiral, solenoid, or discreet inductors.Wherever the interdigital capacitors are used, such capacitors can beduplicated with respect to the corresponding other interdigitalcapacitors. In one connector, some of the interdigital capacitors can beimplemented on a single metalized layer or on several metalized layers.

Although the present invention has been explained by the embodimentsshown in the drawings described above, it should be understood to theordinary skilled person in the art that the invention is not limited tothe embodiments, but rather that various changes or modificationsthereof are possible without departing from the spirit of the invention.

1. An electrical connector, comprising a plurality of input terminals; aplurality of output terminals; a plurality of conductive pathsconnecting respective of the plurality of input terminals withrespective of the plurality of output terminals and a first compensationstructure that couples a first compensating crosstalk signal from afirst of the plurality of conductive paths to a second of the pluralityof conductive paths; and a second compensation structure that couples asecond compensating crosstalk signal from a third of the plurality ofconductive paths to the second of the plurality of conductive paths,wherein the second compensation structure comprises a capacitor and aninductor that is connected to the capacitor in series.
 2. The electricalconnector of claim 1, wherein the inductor comprises a conductive paththat includes one or more self-coupling sections.
 3. The electricalconnector of claim 2, wherein the first compensating crosstalk signalhas a first polarity and the second compensating crosstalk signal has asecond polarity that is generally opposite the first polarity.
 4. Theelectrical connector of claim 2, wherein the conductive path thatincludes one or more self-coupling sections comprises a conductive pathin the general shape of a spiral.
 5. The electrical connector of claim1, wherein the electrical connector comprises an RJ-45 style jack, andwherein a signal input onto the second conductive path from an RJ-45style plug that mates with the RJ-45 style jack reaches the firstcompensation structure before the signal reaches the second compensationstructure.
 6. A printed circuit board for an RJ-45 style electricalconnector, the printed circuit board comprising: a plurality of inputterminals; a plurality of output terminals; a plurality of conductivepaths connecting respective of the plurality of input terminals withrespective of the plurality of output terminals; and a first conductivetrace branching off of a first of the plurality of conductive paths, thefirst conductive trace including a self-inductive section and a firstelectrode of a capacitor; a second conductive trace branching off of asecond of the plurality of conductive paths, the second conductive traceincluding a second electrode of the capacitor.
 7. The printed circuitboard of claim 6, further comprising a first compensation structure thatcouples a first compensating crosstalk signal from the first of theplurality of conductive paths to a third of the plurality of conductivepaths.
 8. The printed circuit board of claim 7, further comprising asecond compensation structure that couples a second compensatingcrosstalk signal from the second of the plurality of conductive paths tothe first of the plurality of conductive paths, wherein the secondcompensation stage includes the capacitor.
 9. The printed circuit boardof claim 8, wherein the first compensating crosstalk signal has a firstpolarity and the second compensating crosstalk signal has a secondpolarity that is generally opposite the first polarity.
 10. The printedcircuit board of claim 6, wherein the self-inductive section of thefirst conductive trace comprises a spiral section of the firstconductive trace.
 11. The connector of claim 6, wherein the capacitorcomprises a parallel plate capacitor.
 12. The connector of claim 6,wherein the capacitor comprises an interdigital capacitor.
 13. A methodof reducing near end crosstalk in an electrical connector that includesa plurality of pairs of conductors, the method comprising: providing afirst compensation structure that couples a first compensating crosstalksignal from a first conductor of a first of the pairs of conductors to afirst conductor of a second of the pairs of conductors; providing asecond compensation structure that couples a second compensatingcrosstalk signal from the first conductor of the first of the pairs ofconductors to a second conductor of the second of the pairs ofconductors; wherein the second compensation structure includes a seriesinductor-capacitor circuit.
 14. The method of claim 13, wherein theinductor in the series inductor-capacitor circuit comprises a conductivepath that includes one or more self-coupling sections.
 15. The method ofclaim 14, wherein the conductive path that includes one or moreself-coupling sections comprises a conductive path in the general shapeof a spiral.
 16. The method of claim 15, wherein the first compensatingcrosstalk signal has a first polarity and the second compensatingcrosstalk signal has a second polarity that is generally opposite thefirst polarity.
 17. An electrical connector, comprising a firstconductor; a second conductor; and a circuit that is configured tocouple energy between the first and second conductors; wherein thecircuit comprises a capacitor and an inductor that is connected inseries to the capacitor.
 18. The electrical connector of claim 17,wherein the first conductor is part of a first differential pair ofconductors and the second conductor is part of a second differentialpair of conductors.
 19. The electrical connector of claim 18, whereinthe inductor comprises a conductive trace on a printed circuit boardthat include self-coupling sections.
 20. The electrical connector ofclaim 19, wherein the conductive trace that includes the self-couplingsections comprises a conductive trace that is in the general shape of aspiral.